Electric lamp having in situ molded base of foamed plastic



Nov. 26, 1968 PLA E 3,413,511 v ELECTRIC LAMP HAVING IN SITU MOLDED BASEOF FOAMED PLASTIC Filed June 1, 1966 1 l2 n a s r e 6 l Q f:;.5 1: :1,'-1;-. .1\1-24 QC: 0 I Q |6 s: Q02 3b l8 o o I 23 I420 20 14 23 F I62 26FIGS.

WITNESSES INVENTOR Vernon L. Plagge AGEN United States Patent 3,413,511ELECTRIC LAMP HAVING IN SITU MOLDED BASE OF FOAMED PLASTIC Vernon L.Plagge, East Orange, N.J., assignor to Westinghouse ElectricCorporation, Pittsburgh, Pa., a corporation of PennsylvaniaContinuation-impart of application Ser. No. 473,028, July 19, 1965. Thisapplication June 1, 1966, Ser. No. 554,493

6 Claims. (Cl. 313-318) ABSTRACT OF THE DISCLOSURE An electricincandescent or fluorescent lamp is provided with a base composed offoamed plastic that is molded in situ on and bonded directly to the endof the lamp envelope. The lead-in conductors are partly embedded in thefoamed plastic base and constitute, or are connected to, contact membersanchored in the plastic. In the case of an incandescent lamp and a screwtype base, one of the lead-in conductors is located at the bottom of thebase threads and constitutes an engagable side contact. A mold is placedin surrounding and abutting relationship with the end of the envelope, afoamable plastic resin is introduced into the mold cavity and isactivated by heat, and the mold is removed after the resulting foamedplastic base has cured and rigidifled.

This application is a continuation-in-part of application Ser. No.473,028, filed July 19, 1965, entitled Electric Lamp Base and Method ofManufacture, and now abandoned.

The present invention relates to electric lamps and, more particularly,to an electric lamp having an improved base and terminal structure.

Heretofore in the art it has been the customary practice to form plasticbases for fluorescent lamps by compression molding a suitable resin in adie. These separately-fabricated bases, which usually are made from athermosetting plastic such as a phenolic condensation product or thelike, are then provided with one or more hollow metallic contact pinsthat are staked or riveted to the bottom of the base shell. After thelamp has been scaled and tipped off, the lead-in wires are threadedthrough the pins and the preformed plastic bases are then cemented tothe ends of the tubular glass envelope. The protruding ends of the leadwires are then severed and the pins are joined to the leads by weldingor soldering. The separate production operations of base forming,cementing, etc., together with the additional transportation costs intransferring the bases from the molding machines to the lamp-basingmachines, increase substantially the overall manufacturing cost offluorescent lamps.

It is accordingly the general object of the present invention to reducethe manufacturing cost of electric lamps by utilizing a base structurethat is formed as an integral part of the lamp itself rather than as aseparate lamp component.

Another object of the present invention is to provide a lamp having abase that is composed of a suitable thermosetting plastic material andcan be formed as an integral part of the lamp to provide an improvedlow-cost base and terminal structure.

The foregoing objects of the present invention, together with otherobjects which will become apparent to those skilled in the art from thefollowing description, are achieved by molding a plastic base directlyonto the end of the lamp envelope. In the case of a fluorescent lamp,this is achieved by providing a mold having a cavity shaped anddimensioned to conform to the outside configuration and dimensions ofthe desired base. The mold has suitable openings into which the hollowbase pins are placed and, thereafter, a predetermined amount of plasticresin and a foaming agent are introduced into the mold. The mold is thenfitted around the sealed-in end of the tubular fluorescent lamp envelopeand the lead-in wires simultaneously threaded through the contact pins.The mold assembly is then heated to a suitable temperature so that thecontained resin foams and fills the mold cavity, thereby conforming tothe contour thereof. At the same time, the resin contacts and adheres tothe surface of the vitreous envelope and the contact pins :and finallycures to a rigid cellular structure. The assembly is subsequentlyallowed to cool and the mold is removed from about the lamp end, leavinga finished base firmly aflixed to the envelope and contact pins.

A better understanding of the invention will be obtained by referring tothe accompanying drawing, wherein:

FIGURE 1 illustrates a completed fluorescent lamp provided with a basestructure at each end formed and applied thereto in accordance with thepresent invention;

FIG. 2 is an enlarged fragmentary crosssectional view of the mold and asealed end of the fluorescent lamp seated therein just after the plastichas expanded into place around the lamp envelope and the base pins;

FIG. 3 is an elevational view of an incandescent lamp having anintegrally-formed base according to the invention; and

FIG. 4 is an enlarged cross-sectional view of the basal end portion ofthe incandescent lamp shown in FIG. 3.

Referring now more specifically to the drawing, in FIG. 1 there is showna fluorescent lamp 5 which comprises the customary tubular vitreousenvelope 6 having a suitable ultraviolet-responsive phosphor coating 7on its interior surface and a pair of oppositely disposed electrodes 8that are supported within the envelope adjacent the ends thereof by apair of lead-in wires 9 and 10 and a vitreous stem 11. Attached to eachsealed end of the envelope 6 in accordance with this invention is aplastic base member 12 of generally cylindrical configuration. Each base12 is provided with a pair of rigid terminals such contact pins 14 towhich the lead-in wires 9, 10 are connected for transmitting electricalenergy to the interiorly disposed electrodes 8. The base 12 at each endof the lamp is secured to the glass surface of the tubular envelope 6 bydirect union therewith entirely independent of any cement or other suchmaterial whatsoever, since the base 12 itself is formed in situ on theend of the envelope.

By reference now more particularly to FIG. 2, it will be noted that amold 16 of resilient material such as silicone rubber or the like istherein shown which has a cavity 17 conforming to the shape anddimensions desired for the finished base 12 This mold may, if desired,be reinforced by a thin outer metallic casing 18. The mold 16 isprovided with a pair of elongated recesses 20 into which the hollowmetallic contact pins 14 are inserted with their upper flared endsspaced slightly above the inner surface of the mold, as shown in thedrawing. A predetermined amount 22 of a suitable thermosetting plasticresin and a foaming agent are then introduced into the mold cavity 17,after which the end of the sealed and exhausted lamp envelope 6 isinserted into the mold 16 by threading the outer exposed ends oflead-wires 9 and 10 through the respective contact pins 14 until theshoulder of the envelope seats against the peripheral edge of theresilient mold and forms a seal therewith.

The lamp and mold assembly is then vertically supported upon blocks 23,or other suitable members, in a surrounding furnace 24 and heated to atemperature rang ing from approximately 50 C. to 0, depending on thetype of plastic resin used. Such heating is continued until the resin 22foams and fills the mold cavity 17 and thereby contacts and covers theends of the envelope 6 and pins 14 disposed within the mold 16. The gasand excess foamed material are discharged through a vent tube 26extending from the bottom of the cavity 17 to the outside of the furnace24. The foamed resin then cures to a rigid cellular structure within ashort period of time, the length of which depends upon the temperatureand particular type of plastic resin employed, leaving the lamp base 12of the desired configuration firmly bonded to and locked in place on thesealed end of the glass envelope 6 and with the contact pins 14 firmlyanchored therein. Since the foamed resin surrounds the outer ends of thelead-in wires 9 and 10 and partly fills the end of the reentrant stem11, as shown in FIG. 2, it aso serves as an insulator that locks thewires in spaced apart relationship and thus prevents short circuits fromdeveloping within the base.

The resin 22 may be of any suitable thermosettingelectrically-nonconductive type plastic, such as a phenolic condensationproduct, a polyvinyl chloride, an epoxy, or the like, while (whenadmixed with a suitable foaming agent such as benzene sulfonyl hydrazideor other nitrogen blowing agent) will foam when heated to an elevatedtemperature. The foaming agent in this case can be introduced separatelyinto the mold cavity 17 through the vent tube 26.

However, the base 12 can just as readily be formed by using a materialthat consists of a mixture of resin and a foaming agent which willlikewise foam when heated to an elevated temperature. Such foamingplastics are well known in the chemical art and comprise polyurethanefoams, polystyrene foams, epoxy foams, silicone foams, cellulose acetatefoams, etc. Foaming plastics of various kinds are described in detail inan article entitled Plastic Foams, May 1966 issue of MaterialsEngineering magazine (vol. 63, No. 5, pp. 87-102). Any of the materialsreferred to in the aforesaid article can be used. The only limitationsare that the plastic be of the type which cures to a hardened rigidcellular structure that is not too porous as to weaken the base 12 tothe extent that it will crack when the contact pins 14 are subjected tothe strain normally encountered in inserting and removing the lamp fromits fixture sockets, and that the plastic be electrically non-conductiveto avoid short-circuiting the lead wires. Of course, the plastic shouldalso be of a type that will remain sufliciently rigid at the operatingtemperature of the lamp that it will support the lamp in its socket.

Preferably the plastic resin, whether self-foaming or one which requiresa separate foaming agent, is selected so that it is completely cured ina relatively short period preferably within ten to fifteen minutes) to ahardened strong base member having a minimum of voids which, if they dooccur, are of minute size. Also, the cooling time should likewise be ofshort duration to enable removal of the base lamp from the mold 16 assoon as possible preparatory to the formation of a base on another lampenvelope. If the times for curing and cooling the plastic are notexcessive, the actual molding of the base 12 directly on the end of thelamp 5 can very readily be done on an automatic lamp-making machine byperforming the molding, curing and cooling operations at various workstations to which the lamp-making machinery is periodically indexed.

After the base lamp 5 is removed from the mold 16, the protruding endsof the lead-in wires 9 and are trimmed and the wires are attached to thepins 14 by welding or the like in the usual manner.

The invention can also be utilized in the manufacture of incandescentlamp types with the same functional, cost and manufacturing advantages.As shown in FIG. 3, a lamp of this type having the usual pear-shapedenvelope 26, and filament mount 28 is provided with a screw-type plasticbase 30 that is molded in situ directly onto the sealed end of theenvelope. As shown more particularly in FIG. 4, one of the lead wires 31connects with a rivet-like member 32 anchored in the end face of thebase to provide an end contact, whereas the other lead 33 is positionedat and is partly exposed by the base threads to provide the necessaryside contact.

It will thus be apparent from the foregoing that a base structure for anelectric lamp, such as fluourescent or incandescent lamp, has beenprovided which is actually molded in place directly onto the end of theenvelope and hence is securely fastened to and forms an integral part ofsuch envelope. Moreover, a method and apparatus for molding the basedirectly on the lamp end has been described which enables the base andterminal structure to be formed on and as part of the operation of anautomatic lamp-making machine, thereby materially reducing themanufacturing cost of both the base and lamp.

Although several embodiments have been herein shown and described, it isto be understood that still further modifications thereof can be madewithout departing from the spirit and scope of the invention. Forexample, a single-ended incandescent lamp could be based by using afoamable resin as a mean for cementing a metal base shell to the bulb,which resin would also seWe as the insulator member at the bottom of theshell and hold the eyelet or end contact in operative relationship withhe shell. In addition, a translucent or color-coded base can veryreadily be provided for fiuorcescent lamps simply by selecting theproper type of plastic resin.

The mold can also be made from any suitable material, providing it doesnot stick to the cured plastic or otherwise interfere with the removalof the formed base. In addition, incandescent lamps can be provided withvarious types and shapes of all-plastic bases simply by altering theconfiguration of the mold cavity. Thus, plastic bases of complex shapes,such as those for miniature lamps of the type designed for use inconjunction with panels having printed electrical circuits and disclosedin US. Patents No. 2,892,992 issued June 30, 1959, can also be readilyfabricated in situ in accordance with the present invention.

I claim:

1. In an electric lamp, the combination comprising:

a vitreous envelope having an end portion that is susceptible tobreakage when stressed and has a deformable conductor dependingtherefrom,

a base member of foamed insulating plastic bonded directly to saidenvelope end portion and holding the conductor in fixed positionrelative to the envelope, and

a terminal anchored in said base member and electrically connected tosaid conductor.

2. The combination of claim 1 wherein said base member is composed offoamed thermosetting plastic.

3. The combination of claim 1 wherein:

said envelope contains an incandescible filament,

said conductor comprises one of a pair of lead wires that are connectedto said filament and are sealed through said envelope end portion, and

said foamed plastic base member is composed of cured thermosetting resinand is molded in situ onto said envelope end portion.

4. The combination of claim 3 wherein:

said base member is of the screw-in type,

the outer ends of said lead wires are embedded in the base member,

one of said lead wires is connected to a terminal anchored in the freeend of the base member, and

the other of said lead wires is located in the threaded portion of saidbase member and constitutes an engageable second contact for the lamp.

5. The combination of claim 1 wherein:

said envelope is of tubular configuration and the said end portioncomprises a sealed end thereof,

said base member encircles the sealed end of the envelope and is moldedin situ thereon, and

said conductor comprises a lead wire that extends from the sealed end ofthe envelope and is connected to a rigid terminal that is anchored inand protrudes beyond the end face of said base member.

6. The combination of claim 5, wherein:

said lamp comprises a fluorescent lamp,

said base member is composed of cured thermosetting resin,

a second lead wire extends from the sealed end of the envelope,

parts of the lead wires are embedded in said base member which thusserves as an insulator, and

said lead wires are connected to a pair of rigid terminals anchored inthe end face of said base member.

References Cited 2,771,589 11/1956 Thomas 313-318X 6 2,884,555 4/1959Peterson 313-318 X 3,010,045 11/1961 Plagge et al 313-318 X 3,218,50011/1965 Wright et al. 313-318 X 3,322,992 5/1967 Parker et a1 313-315 X2,983,838 5/1961 Pechy 313-318 3,077,022 2/1963 Cullis 313-317 FOREIGNPATENTS 413,127 7/1931 Great Britain.

OTHER REFERENCES IBM Technical Disclosure Bulletin, Packaging ofMiniature Lens-End Lamps, by R. J. Keller et a1., vol. 7, No. 5, October1964, p. 399 (copy in group 250, class 313, subclass 318). 15

JOHN W. HUCKERT, Primary Examiner. A. J. JAMES, Assistant Examiner.

